Breakdaddy said:To me, this might tend to add back some of the complexity that slows down 3.x games. In and of itself it seems fine, but add a few more rules like this and you just about might as well pick up 3.x and play it again.
<shudder> No, I don't want to do that!
I'm thinking that this would be a CK call. Most of the time, the spell would simply be cast--no attacks of opportunity, no CON checks. But if the situation seems to call for it, the CK could call for a check.
Of course, there is still Scadgrad's point about this making spellcasters too powerful. I will see how it goes...